linux-kernel - [PATCH v2 2/8] locking/rwsem: Enforce queueing when HANDOFF

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Date:   Mon, 27 Mar 2023 16:24:07 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/8] locking/rwsem: Enforce queueing when HANDOFF

From: Peter Zijlstra <peterz@...radead.org>

Ensure that HANDOFF disables all spinning and stealing.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/locking/rwsem.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index e589f69793df..4b9e492abd59 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -468,7 +468,12 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
 					adjustment -= RWSEM_FLAG_HANDOFF;
 					lockevent_inc(rwsem_rlock_handoff);
 				}
+				/*
+				 * With HANDOFF set for reader, we must
+				 * terminate all spinning.
+				 */
 				waiter->handoff_set = true;
+				rwsem_set_nonspinnable(sem);
 			}
 
 			atomic_long_add(-adjustment, &sem->count);
@@ -755,6 +760,10 @@ rwsem_spin_on_owner(struct rw_semaphore *sem)
 
 	owner = rwsem_owner_flags(sem, &flags);
 	state = rwsem_owner_state(owner, flags);
+
+	if (owner == current)
+		return OWNER_NONSPINNABLE;	/* Handoff granted */
+
 	if (state != OWNER_WRITER)
 		return state;
 
-- 
2.31.1